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Building a ZS6BKW

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N6UM, May 31, 2021.

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  1. N6UM

    N6UM XML Subscriber QRZ Page

    I think I remember reading somewhere that you could tune this antenna two different ways. Either by trimming the wire or by trimming the ladder line. Is this true? Because if that's the case. That would make life easier. I could get the wire close enough. Id be able to trim the ladder line easier.
    WA5RML likes this.
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

  3. K7JOE

    K7JOE Subscriber QRZ Page

    I find trimming the ladder line works pretty well to dial in the antenna -- Mike is correct trimming both is best.
    In practice, I try trimming the ladder line first because I'm lazy ... Usually that gets the close enough - If not, you know you need to lower the radiating elements and trim it a bit.
  4. AF7ON

    AF7ON Ham Member QRZ Page

    There is a range of lengths of antenna elements and feed line that enable matching on most bands - you can find the diagram in Brian Austin’s articles. In making the smaller span “T” version, I chose element lengths of 15 meters with the outer 7.5 meters vertical. With an approximately 400 ohm feed line, I found a good match by trimming it to the length suggested in Brian’s diagram.

  5. W3TKB

    W3TKB XML Subscriber QRZ Page

    As someone who is thinking about his next antenna project being the ZS6BKW, I have a couple questions. Sorry if these are overly rudimentary.

    1. Brian Austin's articles referenced there a link available to these or just do a Google search?
    2. Is the length of coax between antenna and rig a critical factor in this design's performance? I know some antennas (like the G5RV) specify a short run of 20 feet or less. Mine is 130 feet of LMR400; is that too excessive for this antenna?
    3. When trimming ladder line, do you cut from the ends and re-solder to the connections, or take chunks out of the middle and reconnect the wires to each other (twisting, crimping, soldering)? I only ask because my soldering skills aren't the greatest.

    Thanks for the info.
  6. M0AGP

    M0AGP Ham Member QRZ Page

    Vic - I’m not answering your question but just giving you a bit of info that stopped me from putting one up, in case helpful. I was about to buy all the stuff I needed to make one of these, and then checked out the radiation patterns I was seeing in EZNEC antenna software: despite being up over a half wavelength in the middle, my inverted vee version was a cloud warmer - the main radiation lobe was straight up! And this was true on 20 meters on up.

    My center support would have been at about 40 feet and the apex angle about 120 degrees.

    I had assumed that the change from flat format (wire about parallel to the ground) to inverted vee format would be analogous to the change you see in a halfwave dipole when you make it an inverted vee. Not at all!

    The above info refers to the theoretical radiation pattern, which can be different from theory, but I think others on the forum will agree that this is a known effect with the ZS6BKW.
  7. K7JOE

    K7JOE Subscriber QRZ Page

    I'll respectfully disagree based on my practical implementation and self-observed conclusion. I have one at 65 ft, a half wavelength on 40M at the apex and incident angles at about 120ft and it rocks on 40M and 20M ... it does quite well on 17M too. I do experience some lobes on 20 and 17, as expected with an extended / double zepp antenna. No way to really measure the end-fire gain, but it is apparent compared to prior antennas. It does equally well on 40 and 20M as a dipole at similar height as judged by reports from the reverse beacon network, and my own A/B receive switching.
    M0AGP likes this.
  8. M0AGP

    M0AGP Ham Member QRZ Page

    Great that it works for you! What kind of apex angle do you think you have? Or was that 120 degrees?

    It would be interesting to see the radiation pattern modelled. Maybe when it is up 65 feet in the middle that is enough to get it to work on the high bands?

    I wonder how the radiation pattern of the inv vee version of the ZS6BKW looks in "free space"?

    In theory, theory and practice agree, but in practice they may not... :)
  9. K7JOE

    K7JOE Subscriber QRZ Page

    Keep in mind the higher band that the ZS6BKW works on is 10M...and you can usually work the world with a wet noodle on 10M (or a beam isn't too big anway)... It's really designed for 40M and works as an EDZ on 20M (which of course will have a gain pattern off the ends on 20M).... No different than an EDZ dipole on 20M...there are some lobes off the ends of the antenna giving the antenna gain in certain directions, just like the book says. On 17M, it acts almost the same as 20M near as I have observed. So that leaves 10M...and maybe 6M ...but at that point, the antenna alternatives are physically small enough that it might be just as easy to use a different antenna on those two bands. But yes, at 65ft on 10M, i can work everything that i hear...and it hears very well.
    M0AGP likes this.
  10. M0AGP

    M0AGP Ham Member QRZ Page

    Interesting - it must be the added height that "fixes" the radiation pattern. Good to know

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